70duster 360 gets hotter the faster i go

It's not the lack of vacuum advance.

I've been running the 318 in my Challenger without the vacuum advance pretty much since I got it, over 50k miles ago. I run it at 20* advanced at idle, 36* all in mechanical at around 3k. It has a stock 26" 2 core with a straight mechanical fan (no clutch), 180* thermostat. Stock 904, stock convertor. Hooker headers, eddy streetmaster 318 intake, 600 cfm eddy carb. I've never had a problem with it overheating, even when its 110* F out. I pulled the vacuum advance because it would ping each and every single time I accelerated. I went with less advance, which it hated, I went with heavier springs, which it hated, and I dialed back the vacuum advance, which wasn't enough. Don't know. I'm sure I'm losing fuel mileage, even though I typically get 16-17 mpg highway. But overheat? Nope. Never.

The 340 in my Duster sounds more like the 360 in question, 9.8:1 compression, KB 143's, .060" over, ported iron heads with 2.02/1.60's, Lunati 60404 .513/.533, 234/242 @ .050", 110* lobe separation. Doug's headers to 2.5" exhaust, Eddy rpm air gap, now has a holley 750 DP. 4 speed. Has a Mallory unilite electronic dizzy I picked up from another member, which doesn't have the provision for vacuum advance. I run it at 22* advanced, 35* all in at 2,800. It has a 26" 3 core Champion aluminum radiator with a Ford Contour dual electric fan set up. 180* thermostat. Stock 22" radiator support. Never runs hot, fans don't even run constantly when its 110* F out. It does have a high volume water pump.

I'm not saying that running it without the vacuum advance can't be a contributing factor, but it's definitely not the whole problem.